Field of the Invention
The present invention relates to an image recording and reconstructing method, and in particular to a holographic image recording and reconstructing method.
The Prior Arts
In general, the basic principle of producing a holographic film is as follows: firstly, using an image fetching device, such as a charge-coupled device (CCD) camera, to fetch images of an object placed on an object table. Meanwhile, using a light emitting device, such as a Laser, to emit a coherent light to a light splitting module, which splits the light into an object light and a reference light. Wherein, the object light travels along an object light path, to transmit the image fetched by the image fetching device onto a holographic film. In addition, the reference light travels along a reference light path, and is reflected onto the holographic film. Then, the object light and the reference light arrive on the holographic film at the same time to interfere with each other, hereby generating a plurality of dark and bright interference fringes. Then the holographic film thus obtained is developed into a composite holographic film having images of an object recorded thereon. For which, a reference light can be used as reconstruction light to irradiate thereon, to reconstruct a 3D image of the object.
The conventional composite hologram includes cylinder type composite hologram and cone type composite hologram. For which, in recording images or in reconstructing images, the holographic film has to be bent into cylinder shape or cone shape. Therefore, the images thus reconstructed will have distortion and is not satisfying. To redress this problem, a disc type composite hologram is proposed. Yet, regardless the cylinder, cone, or disc type composite hologram, a cylindrical lens has to be used. The composite holographic film thus produced is of a long and narrow sector shape, while the reconstructed image is formed by combining the reconstructed images of a plurality of small composite holographic films, therefore, it is liable to have aberration. Further, on the reconstructed image is overlapped a plurality of gratings, referred to as grating effect, so the quality of the image is inferior.
Moreover, even if a disc type composite hologram is used, since in recording an image, repeated exposures are required, such that the luminance of the reconstructed image is insufficient and it can not be viewed clearly, thus size of the reconstructed image can not be made sufficiently small (for example, to be used as an anti-counterfeiting tag), as such its application is rather limited. Therefore, the image produced by the disc type composite hologram is still not satisfying.
Therefore, presently, the design and performance of holographic image recording and reconstructing method is not quite satisfactory, and it leaves much room for improvement.